1. Field
The present disclosure relates to a developing device used in an image forming apparatus using an electrophotographic method.
2. Description of the Related Art
An electrophotographic image forming apparatus, which is employed in a digital copier or printer, forms an electrostatic latent image by exposing to light a surface of a photosensitive drum which is uniformly charged, forms a visualized toner image by developing the electrostatic latent image with a toner, and records an image by transferring the toner image on a recording medium. In such an image forming apparatus, a two-component developer having, for example, a toner and a carrier is used to develop an electrostatic latent image by attaching the toner charged via a developer bearing member to a surface of a photosensitive drum.
In the developing device, for example, a stirring and carrying unit stirring and friction-charging a toner in the developer while carrying the toner, and a supplying and carrying unit supplying the charged toner to a developer bearing member while carrying the charged toner are installed. The stirring and carrying unit and the supplying and carrying unit may be disposed, for example, in a horizontal direction or a vertical direction. In a developing device in which the stirring and carrying unit and the supplying and carrying unit are disposed in a vertical direction, when a developer is carried to an end of the stirring and carrying unit by a carrying screw, the developer is lifted upward by a carrying pressure thereof and thus is carried to the supplying and carrying unit (e.g., see Japanese Patent Publication No. 2009-25724). Also, there is known a technology to lift a developer upward by a magnetic force such that the developer is easily carried between the stirring and carrying unit and the supplying and carrying unit disposed in a vertical direction (e.g., see Japanese Patent Publication No. 10-31363).
For example, in case the supplying and carrying unit is disposed above the stirring and carrying unit, the amount of the developer lifted by a carrying pressure or a magnetic force is not sufficiently secured, so that a large amount of developer may stay within the stirring and carrying unit. Therefore, a sufficient mixing, stirring and the like of the developer may be hindered, thus resulting in a decline in image quality.